How should I sleep to prevent shoulder and elbow pain?

Essentially, this boils down to experimenting with propping up or supporting your arm, shoulder, or wrist with towels or pillows to relieve stress to your shoulder or elbow. When doing so, begin with your favorite sleeping position as this is the one you are most likely to return to while asleep. Try the following recommendations to fix your sleeping habits:

Lying on your side makes your bottom shoulder slide forward underneath you (abduction). This should be avoided -- especially if you've found that your scapula (shoulder blade) is sitting too far from your spine. The best way to manage this is to try to position the scapula underneath and behind you, so it doesn't slide forward. If that fails, try sleeping on the other side and resting your top arm on a pillow to prevent excessive shoulder blade abduction.

If you are used to sleeping on the painful shoulder, then experiment by propping up the affected side's wrist on pillows (bringing it off the bed) and note whether this decreases your pain. This essentially brings it into more internal rotation and should reduce stress to the shoulder joint.

When sleeping on your back, tight chest muscles or biceps muscles can pull your arm bone forward in your shoulder socket, contributing to an anterior glide (when a bone in a joint slides forward in a socket more than it should normally slide). To reduce this stress and correct this, place your arm on a pillow.

If you sleep on your stomach, place pillows underneath each shoulder to reduce the forward pull of gravity. This will also put the head of the humerus (upper arm bone) in a better position in the shoulder socket.